Quality of Service, Setting Packet Priority 183
ID: um_t2gateway CP560 DVB-T2 Gateway User’s Manual Rev. 2.2 (3686)
Appendix D Quality of Service, Setting
Packet Priority
Normal IP routing is by best effort. This does not work well for broadcast television as the
video and audio components need to be transported as a continuous flow of packets without
interference from other traffic over the internet. There are different techniques to improve
quality-of-service. The main ones are:
• MPLS (Multi Protocol Label Switching)
• Layer 3 routing priority
• Layer 2 routing priority
D.1 MPLS
In networks running MPLS, the packets are forwarded along a predefined path from an ingress
router to an egress router. Packet switching is then done according to the label and packets will
be switched expediently. The MPLS label is added to the IP packet by the ingress router and
removed by the egress router. The labelling is done on the basis of packet classification.
D.2 Layer 3 routing
An alternative technique to improve QoS is to use layer 3 routing and give video content packets
higher priority than other data. IP packets are put into queues according to their priority.
Packets with high priority are forwarded expediently and have a lower probability of being
discarded due to buffer overflow.
There are two ways to prioritise IP packets; using Differentiated services (Diff-serve) or prece-
dence bits (TOS). Both these methods use the same bits in the IP header and both of them are
in common use.
IP precedence values range from 0 to 7. Diff-serve code point (DSCP) values range from 0 to
63.
Figure D.1 Differentiated services (Diff-serve) and precedence bits (TOS)
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